Two unique bone targeting peptides that were identified in our laboratory potentiate the differentiation of mesenchymal cells in vitro. We have shown this by measuring increases in alkaline phosphatase activity and gene expression for osteocalcin, bone sialoprotein, osterix and RUNX2, moreover, the peptides promote bone repair in critical sized unicortical defects in rat tibias. We have identified the molecular targets for these peptides in mesenchymal cells, and our analysis of the data suggest that certain pathways in bone metabolism are involved through which the peptides exert their osteogenic effects. We now propose to study the anabolic effects of the osteotropic peptides by treating C57BL/6J mice and analyzing changes in bone density and mass with fluorochrome labeling and histomorphometry, microCT and biomechanics. We have chosen the C57BL/6J mouse strain because these mice lose bone mass with age, therefore, the C57BL/6J strain may be useful in exploring, both in vivo and in vitro, the molecular mechanism whereby the peptides have their effect on bone metabolism. A pilot study will determine if this mouse strain is suitable as an alternative to ovariectomized mice to explore the anabolic effect and the molecular mechanism of action of the peptides. We will investigate the effect of two osteotropic peptides that potentiate mesenchymal cell differentiation in vitro and bone repair in unicortical defects in vivo in this mouse model, and study the potential anabolic effects of these novel peptides on bone loss. The peptides will be delivered systemically by subcutaneous injection into C57BL/6J mice. Changes in bone mineral density will be measured, and mechanistic changes with fluorochrome labeling and histomorphometry, microCT and biomechanical testing will be determined. The aims of the project are: 1) to measure changes in mineral density, composition, architecture and biomechanical properties of bone, demonstrate the anabolic effect of the peptides on bone loss in a mouse model and compare with the effect of PTH;2) determine the effect of the peptides on metabolic pathways in cells obtained from mice treated with the peptide. Our studies will address the potential for treating bone loss with small molecules that affect the differentiation of mesenchymal cells in bone. A sound scientific basis will help future investigations lay the foundation for developing potential therapies that prevent osteoporosis. PUBLIC HEALTH RELEVANCE: The objective of this proposal is to investigate the anabolic effect of unique osteogenic peptides on bone mass in C57BL/6J mice. In vivo and in vitro methods will determine the effect of the peptides on changes in bone mass, composition and architecture in these mice, as well as the effect on gene expression on cells from bone and marrow.